JP2008134491A - Polarizer protective film and polarizing plate using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizer protective film improved in adhesiveness to a polarizer film and having excellent optical characteristics and low moisture permeability. <P>SOLUTION: The polarizer protective film comprises a thermoplastic resin containing a (meth)acrylic ester or (meth)acrylic acid constituent and a glutarimide unit, wherein the polarizer protective film has an easily adhesive layer on a surface thereof facing a polarizer film. The polarizer protective film is therefore improved in adhesiveness to a polarizer film, and a polarizing plate excellent in optical characteristics and durability can be obtained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polarizer protective film and a polarizing plate using the same.

  The linearly polarizing plate is an optical material that transmits only linearly polarized light having a specific vibration direction and shields other linearly polarized light. The linearly polarizing plate is widely used as one of components of a liquid crystal display device, for example. A generally used linearly polarizing plate is composed of a polarizer film and a polarizer protective film.

  The polarizer film function of transmitting only the linearly polarized light having a specific vibration direction as described above is exhibited by the polarizer film. The polarizer film generally used is, for example, a film obtained by stretching a polyvinyl alcohol film (hereinafter, polyvinyl alcohol is referred to as PVA) and dyeing with iodine or a dichroic dye.

  In addition to protecting the polarizer film, the polarizer protective film holds the polarizer film and imparts practical strength to the entire polarizing plate. For example, a triacetyl cellulose film (hereinafter, triacetyl cellulose is referred to as TAC) is used as a general polarizer protective film. In addition, a polarizer protective film may be called a support body or a support body film in the industry.

  In the polarizer protective film, a film having an unnecessary retardation is generally not preferable. This is because even if the polarizer film has a highly accurate linear polarization function, the retardation of the polarizer protective film and the optical axis shift give the elliptically polarized light to the linearly polarized light that has passed through the polarizer film. Because it will end up.

  On the other hand, by making the polarizer protective film have a specific retardation value and adding the function as a retardation film to the polarizer protective film, the two required films can be combined into one. Has also been done. By reducing the number of constituent films, the productivity of the liquid crystal display device can be improved, and the thickness, weight, and brightness can be improved.

  The phase difference of the film is determined by taking the direction in which the in-plane refractive index is maximum as the X axis, the direction perpendicular to the X axis as the Y axis, and the thickness direction of the film as the Z axis. nz, where d is the thickness of the film, the in-plane retardation Re = (nx−ny) × d, the thickness direction retardation Rth = | (nx + ny) / 2−nz | × d (|| represents the absolute value) ). The aforementioned TAC film basically has a small in-plane retardation. However, the TAC film is a film that easily generates a phase difference due to the action of external stress, and is a film that has a relatively large thickness direction retardation. For this reason, particularly in a large-sized liquid crystal display device, there is a problem that the contrast in the peripheral portion is lowered.

Attempts have been made to use a film material having a smaller photoelastic coefficient than the TAC film as a polarizer protective film. Further, the polarizing performance of the polarizer film is likely to deteriorate due to moisture absorption. Therefore, the polarizer protective film is also used for suppressing moisture absorption of the polarizer film. However, the high water permeability of the TAC film is not sufficient for the purpose of suppressing moisture absorption. Thus, attempts have been made to suppress moisture absorption of the polarizer film and prevent deterioration of polarization performance by using a film material having a moisture permeability smaller than that of the TAC film as the polarizer protective film. For example (see, for example, Patent Document 1), the moisture permeability at 80 ° C. and 90% RH is 200 g / m ² · 24 hr · 100 μm or less and the photoelastic coefficient is 1 × 10 ⁻¹¹ cm ² / dyne or less. A protective film is disclosed.

  The polarizing plate has a structure in which a polarizer protective film is laminated on one side or both sides of a polarizer film. In the polarizing plate, the polarizer protective film is bonded to the polarizer film via an adhesive. For bonding, a water-soluble PVA adhesive is generally used. In the polarizing plate, it is necessary that the adhesive strength between the polarizer protective film and the polarizer film is sufficiently high. Therefore, it is required for the polarizer protective film that the wettability of the adhesive is good and that the adhesive strength with the adhesive is high. For example, the reason that TAC film is used after saponification treatment by pre-immersing the adhesive surface in alkaline solution is that the wettability of the adhesive is not sufficient when used as it is, or the adhesive strength after bonding This is because there is not enough obtained.

Conventionally, a method of providing an easy-adhesion layer for the purpose of improving the adhesion between the polarizer protective film and the polarizer film has been disclosed. If an example is given (refer patent document 2 and 3), the method of using hydrophilic polymers, such as a hydrophilic cellulose derivative, a polyvinyl alcohol derivative, a natural polymer, a hydrophilic polyester derivative, a hydrophilic polyvinyl derivative, as an easily bonding layer, , A method using a -COOM group-containing copolymer compound, and the like are shown. The polarizer protective film used in these is mainly a TAC film, but sufficient adhesive strength can be obtained by laminating a known easy-adhesion layer on a film made of the thermoplastic resin used in the present invention and bonding it to the polarizer film. There was a problem that could not be obtained.
JP-A-7-77608 JP-A-6-118232 JP-A-6-94915

  The present invention has been made in view of the above-mentioned problems of the prior art, and provides a polarizer protective film having improved adhesiveness with a polarizer film and having excellent optical properties and low moisture permeability. .

  As a result of intensive studies in view of the above problems, the present inventor is a polarizer protective film comprising a thermoplastic resin characterized by containing repeating units represented by the general formulas (1) and (2). The polarizer protective film which has an easily bonding layer on the surface of the side facing a child film was provided. Thereby, adhesiveness with a polarizer film is improved significantly, and the polarizing plate excellent in the optical characteristic and durability can be obtained.

  Since the polarizer protective film made of the thermoplastic resin used in the present invention has excellent optical properties and low moisture permeability, a polarizing plate having excellent optical properties and durability that cannot be obtained by conventional TAC films is obtained. be able to.

  The polarizer protective film of the present invention is characterized by comprising a thermoplastic resin containing repeating units represented by the following general formulas (1) and (2).

（ここで、Ｒ１およびＲ２は、それぞれ独立に、水素または炭素数１〜８のアルキル基を示し、Ｒ３は、炭素数１〜１８のアルキル基、炭素数３〜１２のシクロアルキル基、または炭素数６〜１０のアリール基を示す。）

(Here, R1 and R2 each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R3 represents an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or carbon. Represents an aryl group of formula 6-10.)

（ここで、Ｒ４およびＲ５は、それぞれ独立に、水素または炭素数１〜８のアルキル基を示し、Ｒ６は、炭素数１〜１８のアルキル基、炭素数３〜１２のシクロアルキル基、または炭素数６〜１０のアリール基を示す。）
本発明で使用する熱可塑性樹脂を構成する、第一の構成単位は、下記一般式（１）で表される（以下、グルタルイミド単位と言うことがある）。

(Here, R4 and R5 each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R6 represents an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or carbon. Represents an aryl group of formula 6-10.)
The first structural unit constituting the thermoplastic resin used in the present invention is represented by the following general formula (1) (hereinafter sometimes referred to as a glutarimide unit).

（ここで、Ｒ１およびＲ２は、それぞれ独立に、水素または炭素数１〜８のアルキル基を示し、Ｒ３は、炭素数１〜１８のアルキル基、炭素数３〜１２のシクロアルキル基、または炭素数６〜１０のアリール基を示す。）
好ましいグルタルイミド単位としては、Ｒ１、Ｒ２が水素またはメチル基であり、Ｒ３が水素、メチル基、またはシクロヘキシル基である。Ｒ１がメチル基であり、Ｒ２が水素であり、Ｒ３がメチル基である場合が、特に好ましい。

(Here, R1 and R2 each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R3 represents an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or carbon. Represents an aryl group of formula 6-10.)
As preferred glutarimide units, R 1 and R 2 are hydrogen or a methyl group, and R 3 is hydrogen, a methyl group, or a cyclohexyl group. The case where R1 is a methyl group, R2 is hydrogen, and R3 is a methyl group is particularly preferable.

  The glutarimide unit may be a single type, or may include a plurality of types in which R1, R2, and R3 are different.

  The second structural unit constituting the thermoplastic resin used in the present invention is represented by the following general formula (2) (hereinafter referred to as (meth) acrylic acid ester or (meth) acrylic acid structural unit). is there).

（ここで、Ｒ４およびＲ５は、それぞれ独立に、水素または炭素数１〜８のアルキル基を示し、Ｒ６は、炭素数１〜１８のアルキル基、炭素数３〜１２のシクロアルキル基、または炭素数６〜１０のアリール基を示す。）
好ましい（メタ）アクリル酸エステル又は（メタ）アクリル酸構成単位としては、アクリル酸メチル、アクリル酸エチル、メタクリル酸メチル、メタクリル酸エチル等が挙げられる。これらの中でメタクリル酸メチルが特に好ましい。

(Here, R4 and R5 each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R6 represents an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or carbon. Represents an aryl group of formula 6-10.)
Preferable (meth) acrylic acid ester or (meth) acrylic acid structural unit includes methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate and the like. Of these, methyl methacrylate is particularly preferred.

These second structural units may be of a single type or may include a plurality of types in which R4, R5, and R6 are different.
The content of the glutarimide unit represented by the general formula (1) in the thermoplastic resin is preferably 20% by weight or more of the thermoplastic resin. The preferable content of the glutarimide unit is 20 to 95% by weight, more preferably 40 to 90% by weight, and still more preferably 50 to 80% by weight. When a glutarimide unit is smaller than this range, the heat resistance of the film obtained may be insufficient, or transparency may be impaired. On the other hand, if it exceeds this range, the heat resistance is unnecessarily increased and it becomes difficult to form a film, the mechanical strength of the resulting film becomes extremely brittle, and the transparency may be impaired.

  The polarizer protective film used in the present invention can control the optical anisotropy of the film according to the purpose of use. By increasing the content of the glutarimide unit represented by the general formula (1), the optical anisotropy can be increased. When the function as a retardation film is imparted to the polarizer protective film using this, it is possible by adjusting the composition according to the required retardation value.

  The thermoplastic resin used in the present invention may contain a third structural unit. As the third structural unit, nitrile monomers such as acrylonitrile and methacrylonitrile, maleimide monomers such as maleimide, N-methylmaleimide, N-phenylmaleimide, and N-cyclohexylmaleimide can be used.

    However, the thermoplastic resin used in the present invention does not contain the repeating unit represented by the general formula (3).

（ここで、Ｒ７は水素または炭素数１〜８のアルキル基を示し、Ｒ８は炭素数６〜１０のアリール基を示す。）
本発明で使用する熱可塑性樹脂は、リニア（線状）ポリマーであっても、またブロックポリマー、コアシェルポリマー、分岐ポリマー、ラダーポリマー、架橋ポリマーであっても構わない。ブロックポリマーはＡ−Ｂ型、Ａ−Ｂ−Ｃ型、Ａ−Ｂ−Ａ型、またはこれら以外のいずれのタイプであっても問題ない。コアシェルポリマーはただ一層のコアおよびただ一層のシェルのみからなるものであっても、それぞれが多層になっていても問題ない。

(Here, R7 represents hydrogen or an alkyl group having 1 to 8 carbon atoms, and R8 represents an aryl group having 6 to 10 carbon atoms.)
The thermoplastic resin used in the present invention may be a linear (linear) polymer, or may be a block polymer, a core-shell polymer, a branched polymer, a ladder polymer, or a crosslinked polymer. There is no problem even if the block polymer is A-B type, A-B-C type, A-B-A type, or any other type. There is no problem even if the core-shell polymer is composed of only one core and only one shell, or each layer is a multilayer.

  The thermoplastic resin used in the present invention is a resin having a unit that can be imidized in the same manner as the glutarimide resin described in US Pat. No. 3,284,425, US Pat. No. 4,246,374, JP-A-2-153904, and the like. It is obtained by imidizing a resin having a unit capable of imidization with ammonia or a substituted amine, using a resin obtained using methyl methacrylate as a main raw material.

The thermoplastic resin used in the present invention preferably has a weight average molecular weight of 1 × 10 ⁴ to 5 × 10 ⁵ . If the weight average molecular weight is less than the above value, the mechanical strength in the case of film is insufficient, and if it is more than the above value, the viscosity at the time of melting may be high, and the productivity of the film may decrease. is there.

  The glass transition temperature of the thermoplastic resin used in the present invention is preferably 100 ° C. or higher, more preferably 120 ° C. or higher, and further preferably 130 ° C. or higher.

  If necessary, other thermoplastic resins can be added to the thermoplastic resin used in the present invention.

The thermoplastic resin used in the present invention preferably has a small photoelastic coefficient. The photoelastic coefficient of the thermoplastic resin used in the present invention is preferably 20 × 10 ⁻¹² m ² / N or less, more preferably 10 × 10 ⁻¹² m ² / N or less, and more preferably 5 × 10. More preferably, it is ^-12 m ² / N or less. When the absolute value of the photoelastic coefficient is larger than 20 × 10 ⁻¹² m ² / N, optical distortion occurs due to stress, and light leakage tends to occur. In particular, the tendency becomes remarkable in a high temperature and high humidity environment.

The photoelastic coefficient means that when an external force is applied to an isotropic solid to cause stress (ΔF), it temporarily exhibits optical anisotropy and exhibits birefringence (Δn). The ratio of stress to birefringence is called photoelastic coefficient (c), and the following formula
Indicated by

  As a method for forming the thermoplastic resin into a polarizer protective film used in the present invention, any conventionally known method can be used. Examples thereof include a solution casting method and a melt extrusion method. Any of them can be adopted. The solution casting method is suitable for the production of a film with little resin deterioration and good surface properties, and the melt molding method can obtain a film with high productivity. As a solvent for the solution casting method, methylene chloride or the like can be preferably used. Examples of the melt molding method include a melt extrusion method and an inflation method.

  The thickness of the polarizer protective film used in the present invention is preferably 20 μm to 300 μm, and more preferably 30 μm to 200 μm. More preferably, it is 40 μm to 100 μm. The thickness unevenness of the film is preferably 10% or less, more preferably 5% or less of the average thickness.

  The light transmittance of the polarizer protective film used in the present invention is preferably 85% or more, more preferably 88% or more, and further preferably 90% or more. The turbidity of the film is preferably 2% or less, more preferably 1% or less, and still more preferably 0.5% or less.

  In the present specification, for convenience of explanation, a film after the thermoplastic resin is formed into a film and before being stretched may be referred to as a “raw material film”.

The raw material film can be a polarizer protective film as it is without being stretched, but in the production of the polarizer protective film used in the present invention, after forming the film by the above-mentioned method, it is uniaxially stretched or biaxially stretched. Thus, it can be adjusted to a predetermined phase difference value. The mechanical properties of the film can also be improved by stretching.

The film may be stretched continuously immediately after forming the raw material film. Here, there may be a case where the state of the “raw material film” exists only momentarily. In the case where it exists only momentarily, that momentary state after the film is formed and then stretched is referred to as a raw material film. In addition, the raw material film only needs to be in a film shape sufficient to be stretched thereafter, and does not need to be in a complete film state. Of course, it does not have the performance as a completed film. Also good. Moreover, after shaping | molding a raw material film as needed, you may store or move a film once, and may extend | stretch a film after that. As a method of stretching the raw film, any conventionally known stretching method can be adopted. Specifically, for example, there are longitudinal stretching using a roll or a hot stove, transverse stretching using a tenter, and sequential biaxial stretching in which these are sequentially combined. Moreover, the simultaneous biaxial stretching method of extending | stretching length and width simultaneously is also employable. You may employ | adopt the method of performing lateral stretching by a tenter after performing roll longitudinal stretching.

  The polarizer protective film used by this invention can be made into a final product in the state of a uniaxially stretched film. Furthermore, it is good also as a biaxially stretched film by combining and extending | stretching a process. When performing biaxial stretching, if necessary, the stretching conditions such as the temperature and magnification of the longitudinal stretching and the lateral stretching may be the same, and optically anisotropic to the film by intentionally changing it. May be given.

  The stretching temperature and stretching ratio of the film can be adjusted as appropriate using the optical anisotropy, mechanical strength and surface properties, and thickness accuracy of the obtained film as indices. The range of the stretching temperature is preferably in the range of Tg-30 ° C to Tg + 30 ° C, where Tg is the glass transition temperature of the film obtained by the DSC method. More preferably, it is the range of Tg-20 degreeC-Tg + 20 degreeC. More preferably, it is the range of Tg or more and Tg + 20 degrees C or less. If the stretching temperature is too high, the thickness unevenness of the obtained film tends to be large, and it becomes impossible to provide sufficient optical anisotropy, and mechanical properties such as elongation, tear propagation strength, and fatigue resistance Improvement in properties tends to be insufficient. Moreover, the trouble that the film adheres to the roll is likely to occur. On the other hand, when the stretching temperature is too low, the turbidity of the stretched film tends to be high, and in the extreme case, it tends to cause problems in the process such as tearing or cracking of the film.

  In the case of a polarizer protective film imparted with a function as a retardation film, optical anisotropy can be imparted by performing uniaxial or biaxial stretching according to a required retardation value. The stretching temperature and the stretching ratio can be appropriately adjusted according to the required retardation value.

  The polarizer protective film used in the present invention is a known process additive such as a heat stabilizer, an ultraviolet absorber, a lubricant, or other known additives such as fillers and other polymers, as necessary. May be contained. In particular, a filler may be contained for the purpose of improving the slipperiness of the film. As the filler, inorganic or organic fine particles can be used. Examples of inorganic fine particles include metal oxide fine particles such as silicon dioxide, titanium dioxide, aluminum oxide and zirconium oxide, silicate fine particles such as calcined calcium silicate, hydrated calcium silicate, aluminum silicate and magnesium silicate, Calcium carbonate, talc, clay, calcined kaolin, calcium phosphate, and the like can be used. As the organic fine particles, resin fine particles such as silicon resin, fluorine resin, acrylic resin, and cross-linked styrene resin can be used.

  In addition to improving the weather resistance by adding an ultraviolet absorber to the polarizer protective film used in the present invention, the durability of the liquid crystal display device using the polarizer protective film of the present invention can also be improved, which is practically preferable. . Examples of the ultraviolet absorber include benzotriazole-based ultraviolet absorbers such as 2- (2H-benzotriazol-2-yl) -p-cresol and 2-benzotriazol-2-yl-4,6-di-t-butylphenol, Triazine-based UV absorbers such as 2- (4,6-diphenyl-1,3,5-triazin-2-yl) -5-[(hexyl) oxy] -phenol, benzophenone-based UV absorbers such as octabenzone, etc. Benzoate light stabilizers such as 2,4-di-t-butylphenyl-3,5-di-t-butyl-4-hydroxybenzoate and bis (2,2,6,6-tetramethyl) Light stabilizers such as hindered amine light stabilizers such as -4-piperidyl) sebacate can also be used.

  The polarizer protective film used in the present invention can be subjected to a surface treatment as necessary to improve the affinity with the easy-adhesion layer. As the surface treatment method, any conventionally known method is possible. For example, electrical treatment such as corona discharge treatment and spark treatment, plasma treatment under low or normal pressure, ultraviolet irradiation treatment in the presence or absence of ozone, acid treatment with chromic acid, alkali saponification treatment, flame treatment, etc. Is mentioned. By these methods, the surface tension of the film surface can be increased to 50 dyne / cm or more. By using these surface treatments together with the easy adhesion treatment of the present invention, the adhesive force can be improved. Corona discharge treatment is preferred because of the simplicity of the treatment.

  The easy adhesion layer in this invention means the layer which provides the function which makes it easy to adhere | attach a polarizer protective film and a polarizer film.

  The cellulose ester used in the present invention may be a fatty acid ester of cellulose having hydrolyzability, but is preferably a lower fatty acid ester of cellulose. Lower fatty acid means a fatty acid having 6 or less carbon atoms.

  Specific examples of the lower fatty acid ester of cellulose include, for example, single fatty acid esters such as cellulose diacetate, cellulose triacetate, cellulose propionate, and cellulose butyrate, mixed fatty acid esters such as cellulose acetate propionate and cellulose acetate butyrate, And mixtures thereof. Among these, when using a method of attaching a cellulose ester layer on a film by using a cellulose ester as a solution, the solvent that can be selected is relatively wide, and the surface modification by hydrolysis after the attachment of the layer is easy. Cellulose acetate propionate and cellulose acetate butyrate are preferred.

  The degree of polymerization of the cellulose ester is preferably 100 to 400 as the degree of polymerization of cellulose from the viewpoint of maintaining the strength of the layer.

  The thickness of the cellulose ester layer is not particularly limited, but is preferably 0.1 to 20 μm. If it is less than the above range, the adhesive strength after bonding tends to be stable and difficult to obtain, and if it exceeds the above range, it contributes to the improvement of the moisture and heat resistance of the polarizing plate even if the polarizer protective film has low moisture permeability. This tends to cause practical disadvantages in that it becomes difficult to do so or the thickness of the polarizing plate after bonding becomes thick.

  As a method for forming the cellulose ester layer used in the present invention, for example, a solution or dispersion in which cellulose ester is dissolved or dispersed in water or an organic solvent is applied and dried on the polarizer protective film used in the present invention. After forming a layer or a solution or dispersion in water or an organic solvent together with another thermoplastic resin using cellulose ester as a matrix on the polarizer protective film used in the present invention Examples thereof include a method of forming a layer by drying, a method of forming a layer by applying a thermosetting resin solution in which cellulose ester is dispersed on the polarizer protective film used in the present invention, and then curing the matrix. Among these, a method of forming a layer by applying a solution obtained by dissolving cellulose ester in an organic solvent and drying the solution on a polarizer protective film is preferable from the viewpoint of easy industrial production.

  The organic solvent is preferably capable of producing a fluid by dissolving or dispersing cellulose ester, and preferably has an affinity capable of being cast on the polarizer protective film used in the present invention. For example, the toluene / methyl ethyl ketone mixed solution (weight ratio 1: 1) has an appropriate swelling property for the polarizer protective film used in the present invention in addition to being a good solvent for cellulose ester. Therefore, it is preferable because the interface strength between the cellulose ester and the polarizer protective film can be further increased.

  As a method for applying the solution or dispersion on the polarizer protective film used in the present invention, a method usually used for applying a liquid substance to a solid surface, for example, a gravure coating method, a dip coating method, a spraying method, or the like. The method of apply | coating on a polarizer protective film by the coating method, the casting method, etc. can be used.

  The polarizer protective film of the present invention has a cellulose ester layer-side surface directed to the polarizer film, and is bonded to the polarizer film via an adhesive, preferably an aqueous adhesive. Can be integrated. In the film of the present invention, it is preferable to saponify the surface of the cellulose ester layer with an alkali solution or the like before the bonding. By the saponification treatment, the surface of the cellulose ester layer is hydrophilized, and adhesion with an aqueous adhesive and adhesive strength after drying the adhesive can be improved.

  In order to sufficiently improve the adhesiveness and adhesive strength with the adhesive, the contact angle with the pure water on the surface of the cellulose ester layer is preferably less than 50 degrees. When the contact angle is larger than the above range, adhesion and adhesive strength tend not to be well-balanced.

  The method for the saponification treatment is not particularly limited, but usually a method of immersing the film in an aqueous solution such as sodium hydroxide or potassium hydroxide or an alkaline solution such as a water / alcohol mixed solution, followed by washing with water and drying. Can be used.

  The concentration of the alkaline solution is not particularly limited, but is preferably 1 to 10N. The temperature of the alkaline liquid may be usually 20 to 95 ° C, but preferably 30 to 95 ° C. The time for dipping in the alkaline solution may be appropriately selected according to the concentration / temperature and the desired degree of modification, but can usually be 15 seconds to 20 minutes. When it is desired to further reduce the immersion time, it may be preferable to coexist alcohols such as methanol and ethanol, triethanolamine and the like in the alkaline solution.

  The polarizer protective film of the present invention is directed to the polarizer film with the side having the easy-adhesion layer, bonded to the polarizer film via an adhesive, and integrated with the polarizer film through predetermined drying, A polarizing plate can be created. A known iodine-based or dye-based polarizer film can be used as the polarizer film. As the adhesive, a water-based adhesive mainly composed of a polyvinyl alcohol-based compound can be suitably used.

  The polarizer protective film of the present invention can be subjected to a coating treatment such as a hard coat, an antiglare coat, a non-reflective coat, and other functional coats as necessary.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to this Example.

  Each physical property value of the film was measured as follows.

(1) Quantification of imidation ratio Using the pellet of the product as it was, IR spectrum was measured at room temperature using TravelIR manufactured by SensIR Technologies. Imide from the obtained spectrum, the absorption intensity (Absester) attributed to the ester carbonyl group of 1720 cm ^-1, from the ratio of absorption intensity (Absimide) attributed to imide carbonyl group 1660 cm ^-1, the formula 1 below The conversion rate (Im%) was determined.

（２）ガラス転移温度（Ｔｇ）
生成物１０ｍｇを用いて、示差走査熱量計（ＤＳＣ、株式会社島津製作所製ＤＳＣ−５０型）を用いて、窒素雰囲気下、昇温速度２０℃／ｍｉｎで測定し、中点法により決定した。

(2) Glass transition temperature (Tg)
Using 10 mg of the product, a differential scanning calorimeter (DSC, model DSC-50 manufactured by Shimadzu Corporation) was used and measured at a heating rate of 20 ° C./min in a nitrogen atmosphere and determined by the midpoint method.

(3) Total light transmittance A test piece having a size of 50 mm × 50 mm was cut out from the film. This test piece was measured by the method described in 5.5 of JIS K7105-1981 at a temperature of 23 ° C. ± 2 ° C. and a humidity of 50% ± 5% using a turbidimeter NDH-300A manufactured by Nippon Denshoku Industries Co., Ltd. did.

(4) Turbidity Using the turbidimeter NDH-300A manufactured by Nippon Denshoku Industries Co., Ltd., the test piece obtained in (3) was added to JIS K7105 at a temperature of 23 ° C. ± 2 ° C. and a humidity of 50% ± 5%. Measured accordingly.

(5) In-plane retardation Re and thickness direction retardation Rth
A test piece of 4 cm × 4 cm was cut out from the film. Using an automatic birefringence meter (KOBRA-WR manufactured by Oji Scientific Co., Ltd.), the in-plane retardation Re was measured at a temperature of 23 ± 2 ° C. and a humidity of 50 ± 5% at a wavelength of 590 nm and an incident angle of 0 °. It was measured. The thickness d of the test piece measured using a digimatic indicator (manufactured by Mitutoyo Corporation), the refractive index n measured by an Abbe refractometer (manufactured by Atago Co., Ltd. 3T), the wavelength 590 nm measured by an automatic birefringence meter, and the surface The three-dimensional refractive index nx, ny, nz is determined from the internal phase difference Re and the phase difference value in the 40 ° tilt direction, and the thickness direction phase difference Rth = | (nx + ny) / 2−nz | × d (|| is the absolute value) Represents).

(6) Photoelastic coefficient A test piece was cut out from a film into a strip shape having a width of 15 mm and a length of 60 mm, and using an automatic birefringence meter (KOBRA-WR manufactured by Oji Scientific Co., Ltd.), temperature 23 ± 2 ° C. humidity 50 ± In 5%, it measured at wavelength 590nm. One side of the film was fixed, and the other side was subjected to birefringence measurement in a state where a load was applied every 100 gf from no load to 1000 gf, and a change amount of birefringence due to unit stress was calculated from the obtained result.

  (7) Adhesive layer thickness: The film thickness before and after lamination was measured, and the increased thickness was calculated.

  (8) Adhesive strength: The film was cut into 50 mm in the TD direction and 100 mm in the MD direction, immersed in an aqueous solution of sodium hydroxide (concentration 10% by weight) kept at 60 ± 5 ° C. for 2 minutes, washed thoroughly with water, The polarizer protective film which carried out the chemical treatment was obtained. A polyester adhesive tape (Nitto Denko, No. 31C 75 Hi) was applied to the lower end of the film in the MD direction at 10 mm and the full width in the TD direction (50 mm) to provide a chuck pinch for measuring the adhesive strength. A biaxially stretched PVA film (Nippon Synthetic Chemical Industry, Boblon # 140) was cut out in a TD direction of 50 mm and a MD direction of 100 mm, and a chucking margin was provided at the lower end in the same manner as described above. A 3% by weight aqueous solution of a PVA compound (Kuraray, Poval 117) is applied to the entire surface in the width direction with a pipette on the upper part of the measurement film (the chuck clamping margin is the upper surface). They were superposed so as to face the test film, and pressed with a roller having a weight of 5 kg. This was dried at 80 ° C. for 10 minutes to obtain an adhesive. The adhesive strength of the obtained adhesive was measured with a digital weight meter (Imada, DPRS2TR) (tensile speed was 300 mm / min).

(9) Peeling rate: A PET film (Teijin, Tetron HS-125) was cut into a width of 50 mm and a length of 90 mm, and the weight was measured. The PET film after measurement was overlaid on the adhesive after the adhesive strength test, and the PET film was cut out along the shape where the biaxially stretched PVA film was peeled off. The weight of the PET film cut out in the area where the biaxially stretched PVA film was peeled was measured and designated as weight B. [Poval peel rate] = | weight B / weight A | × 100
Was used to calculate the peel rate of the bonded body after the adhesive strength test.

(Example 1)
A commercially available methacrylic resin (Acrypet VH manufactured by Mitsubishi Rayon Co., Ltd.) was used as an imidizing agent to produce an imidized resin. The extruder used was a meshing type co-rotating twin screw extruder having a diameter of 15 mm. The set temperature of each temperature control zone of the extruder was 230 ° C., the screw rotation speed was 150 rpm, the methacrylic resin was supplied at 1.0 kg / hr, and the supply amount of methylamine was 40 parts by weight with respect to the methacrylic resin. A methacrylic resin was introduced from a hopper, and the resin was melted and filled with a kneading block, and then methylamine was injected from a nozzle. A seal ring was placed at the end of the reaction zone to fill the resin. By-products after the reaction and excess methylamine were devolatilized by reducing the pressure at the vent port to -0.08 MPa. The resin that came out as a strand from a die provided at the exit of the extruder was cooled in a water tank and then pelletized with a pelletizer.

Table 1 shows the imidization ratio and glass transition temperature of the obtained imidized resin. The obtained imidized resin was dissolved in methylene chloride (resin concentration 25 wt%), applied onto a PET film, and dried to prepare a cast film. The cast film was subjected to simultaneous biaxial stretching (biaxial stretching device X4HD, manufactured by Toyo Seiki Co., Ltd.) at a stretching ratio of 2 times (longitudinal and lateral) and a temperature 20 ° C. higher than the glass transition temperature, thereby producing a biaxially stretched film. Table 1 shows the total light transmittance, turbidity, in-plane retardation, and thickness direction retardation of this biaxially stretched film. Moreover, it was 1 * 10 < ^-12 > m < ² > / N when the photoelastic coefficient of this biaxially stretched film was measured.

  On this biaxially stretched film, a solution of cellulose acetate propionate (Eastman Chemical Tenite Propionate 360A) dissolved in a toluene / methyl ethyl ketone mixed solvent (toluene: methyl ethyl ketone (weight ratio) = 1: 1) (concentration: 10 wt. %) Was heat-treated at 120 ° C. for 10 minutes to obtain a protective film in which the cellulose ester layer was laminated on the polarizer protective film. Table 1 shows the performance of the obtained polarizer protective film.

(Example 2)
In Example 1, the surface of the biaxially stretched film was corona treated with a discharge amount of 200 W · mim / m ² , and then a cellulose ester layer was formed in the same manner as in Example 1. Table 1 shows the performance of the obtained polarizer protective film.

(Example 3)
Cellulose acetate propionate (Eastman Chemical CAP-482-20) was mixed with a toluene / methyl ethyl ketone mixed solvent (toluene: methyl ethyl ketone (weight ratio) = 1: 1 on the biaxially stretched film prepared in the same manner as in Example 1. The solution (concentration: 10% by weight) dissolved in) was cast and then heat-treated at 120 ° C. for 10 minutes to obtain a polarizer protective film having a cellulose ester layer laminated on the polarizer protective film. Table 1 shows the performance of the obtained polarizer protective film.

(Comparative Example 1)
A biaxially stretched film prepared by the same method as in Example 1 was used as a polarizer protective film as it was. Table 1 shows the performance of the obtained polarizer protective film.

(Comparative Example 2)
In Example 1, instead of laminating the easy-adhesion layer, the surface of the biaxially stretched film was corona treated with a discharge amount of 200 W · mim / m ² . Table 1 shows the performance of the obtained polarizer protective film.

Claims (5)

A polarizer protective film comprising a thermoplastic resin containing repeating units represented by the following general formulas (1) and (2), and an easy-adhesion layer on the surface facing the polarizer film A polarizer protective film.

(Here, R1 and R2 each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R3 represents an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or carbon. Represents an aryl group of formula 6-10.)

(Here, R4 and R5 each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R6 represents an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or carbon. Represents an aryl group of formula 6-10.) A polarizer protective film made of a thermoplastic resin containing repeating units represented by the general formulas (1) and (2) is subjected to surface treatment on the surface facing the polarizer film, The polarizer protective film according to claim 1, further comprising an easy-adhesion layer. The polarizer protective film according to claim 1 or 2, wherein the easy adhesion layer contains cellulose ester as a main constituent. The polarizer protective film according to claim 3, wherein the cellulose ester is cellulose acetate propionate. The polarizing plate by which the polarizer protective film of Claims 1-4 is laminated | stacked on the at least single side | surface of a polarizer film.